Some people have had trouble finding the top of the Giant's Staircase to descend. Was out there today and there were a few tape markers and a couple of cairns at the top.
In case these disappear or it's dark, here's a GPS reading for the turn-off :
37.190150 S, 142.502186 E

It would be a bit tricky to find from above if you'd never been up there before. I'd suggest anyone new to the area take 10 minutes to walk up and check it out before doing a route. Once you know the features its pretty easy.